At present, a photovoltaic combiner box is mainly applied to a centralized photovoltaic power generation system, as shown in FIG. 1. Generally, a conventional combiner box includes modules such as an input terminal, an output terminal, a circuit breaker, a fuse box, a lightning protection module, detection circuits for voltage, current and temperature, a control system and a switching power supply. The detection circuits of the combiner box can detect parameters such as a voltage and a current inputted by each string, an output voltage, an output current and a box temperature. The fuse box and the lightning protection module are respectively configured for over current protection and surge protection. The control system can send data of the combiner box to an inverter or a client. The circuit breaker is mainly configured to disconnect the inverter in installation or maintenance, to protect safety of an operator.
In a conventional photovoltaic power generation system with a combiner box, output terminals of multiple combiner boxes are generally connected in parallel to a direct current input terminal of one inverter. In a case that a component connected to a certain combiner box needs to be maintained, the combiner box is disconnected from the inverter by using the circuit breaker, while the inverter and other combiner boxes are still in normal operation states.
Since some components in a string corresponding to the combiner box to be disconnected may still generate electricity, a certain impact current and a certain arc may be inevitably generated due to directly switching off the circuit breaker in the combiner box. In addition, in the case that the maintained component is reconnected to the combiner box, the string corresponding to the combiner box outputs an open-circuit voltage. A direct current bus voltage of the inverter is relatively low since the inverter performs maximum power point tracking (MPPT) control. In this case, it is inevitable to generate a certain impact current which burns down a fuse, in connecting two voltage sources with a large voltage difference in parallel.